Non-healing, painful leg ulcers present a major therapeutic challenge in sickle cell disease. We observed that topical application of opioids stimulates angiogenesis and accelerates healing of ischemic wounds in rats. We hypothesize that specific opioid receptor(s) in the wound modulate angiogenesis and healing through distinct cellular and molecular mechanism(s). Thus topically applied opioids might promote healing of chronic painful ulcers in sickle cell disease. We will test this via: Aim # 1: Opioid receptor(s) stimulate pro-proliferative signaling by, [a] transactivating VEGF receptor-2 on endothelial cells, [b] stimulating MAPK/ERK and STAT3 signaling pathway and [c] by mediating the effect of endogenous opioids produced by keratinocytes. AIM # 2: Opioid(s)/opioid receptor(s) in the skin are essential for maintenance of normal skin architecture and are involved in wound healing. We will examine the: [a] alterations in wound healing in opioid receptor(s)/ligand knockout mice to identify the specific opioid receptor(s) involved in wound healing, [b] cell specific opioid receptor(s)/endogenous opioid expression in the wild type vs sickle mouse skin. AIM #3: Topically applied opioids in clinically relevant doses promote: [a] wound healing in sickle mice and [b] analgesia to wound associated nociception. AIM # 4: Stressed and ischemic sickle milieu induced perturbation of the interdependent triad of angiogenesis, lymphangiogenesis and neurogenesis underlies the pathogenesis of non-healing wounds in SCD. We will use an open ischemic wound model that mimics human ischemic skin ulcers. In vivo studies will be performed on transgenic mice expressing sickle hemoglobin mimicking human disease and mice deleted for opioid receptor(s) or ligands, while in vitro experiments will use human dermal microvascular endothelial cells or blood outgrowth endothelial cells from different mice, and keratinocytes. If our hypotheses are true, this project may lead to the development of an effective treatment for painful leg ulcers in sickle cell disease.